Purification of acetylene



Feb. 6, 1934. H. BUECKERT [L ,M y 1,945,592

PURIFICATIQN oF CETYLENE Filed NOV. 19', 19:51V

TTORNEYS Patented Feb. 6, 19734 1,945,592 PURIFICATION F ACETYLENE Hanns Bueckert, Ludwigshafen-on-the-Rhine,

Robert Stadler,

Ziegelhausen, andl Helmut Tanneberger, Mannhei'in, Germany, assignors to 'I. G. Farbenindustrie Aktiengesellschaf Frankfort-on-the-Main, Germany Application November 19, 1931, Serial No.

576,098, and in Germany November 20, i930 3 Claims. (Cl. 1834-115) The present invention relates to improvements in the purification o f acetylene.

The purification of acetylene containing other strongly unsaturated compounds, such as di- 5 acetylene, allylene, aliene or butadiene or several of these substances, especially of the-gas mixtures, containing acetylene obtained by thermal treatment, for example in the electric arc, of

hydrocarbon products of any kind, in particular vaporized hydrocarbons, which term. for the purpose of the present invention comprises gaseous saturated hydrocarbons, such as methane or ethane or the dlike, or unsaturated hydrocarbons of the olenic series, such as ethylene or pro- 16 pylene, or vaporized `liquid aliphatic or cyclic hydrocarbons or the said liquid hydrocarbons in the form of mist, or of liquid hydrocarbons in bulk, for example by passing an electric arc therethrough, or of coals of any variety passed through the electric arc in the forn'i'of dust, is attended with great difilculty.

The electric arc treatment may be replaced by heating the `saidmatenals in a proper form to temperatures above 1000"' C., .preferably above 14:00 C., for example by partial combustion with gases comprising oxygen. Although the amount of the said impurities in acetylene produced in 'the said thermal treatments is usually very small as for example about 0.3 per cent, the impurities injuriously affect the further working up of the acetylene, as for example into acetaldehyde by means of solid catalysts or by means of acid solutions containing mercury. The acetylene cana lnot be freed satisfactorily from the said imlene frdm the gas from the electric arc, because compared with acetylene they have a greater solubility or capacity of being adsorbed by solid absorbing agents so that they are likewise enriched and therefore the gas recovered from the washing liquid or the adsorption agent contains from 2 to 5 per cent ofthe said impurities depending on the amount of impurities in the gas from the electric arc.

We have now found that a satisfactory separation of acetylene from the said strongly unsaturated substances is effected by subjecting the mixture to strong cooling, i. e. cooling to temperatures of 20 below zero C., preferably of 30 below zero C. and below, care being taken that temperatures at which solid acetylene separates are avoided and the conditions being such-that a condensation of acetylene is precluded. 'I'hus for example solid acetylene separates out at 81 below zero C. or at lower temperatures if its purities by washing out or adsorbing the acetypartial pressure attains one atmosphere. By carrying out the cooling as hereinafter described the condensed products may be separated in al liquid state by reason of their mutual solubility,

.although in the case of some of them,as for 00 example diacetylene and hydrocyanic acid, the freezing point lieshigher than the cooling temperature. For example when starting with concentrated,l from 85 to 90 per cent acetylene, the impurities are preferably condensed by cooling 05 to from about to 80 below zero C. without the application of pressure, whereby the solvent vapour present in the acetylene (whichis recovered from the gas mixture issuing from the electricarc by absorption by means of a suitable '(0 solvent, such as cyclohexanone or acetone) may be precipitated at the same time. If diluted acetylene is to be purified in the same manner, v the cooling is carried out at from 70 to 80 below zero C., preferably at increased pressure. ForI 76 example the purication of a from 7 to 9 per cent gas may be eiected at from 15 to 26 atmospheres. Gases vhaving a high concentration of acetylene are advantageously treated under atmospheric pressure because at elevated pressures 80 concentrated acetylene is liable to explode. Contrary to expectation, a separate purication from hydrocyanic acid has proved to be-unnecessary because the hydrocyanic acid contained as an impurity in the acetylene from the electric arc is also almost completely removed by condensation and solution in the other condensed products.

The process according to the present invention may be carried out for example as follows:

The cooling of the gas for example down to temperatures of 30 below zero C. is preferably 'carried out-in several stages in order to eiiect a better separation of the condensed constituents, whereby in theflrst stage the water and, if any, 05 also the solvent vapours contained in the gas mixture are vseparated in the liquid phase, and then the impurities which are gaseous at ordinary temperatures are obtained in a liquid state at lower temperatures. For example if acetylene which has been obtained from dilute acetlyene by enrichment by treatment with cyclohexanone is puried according to the present invention, the solvent contained in the gas is condensed and recovered in the first stage of the cooling (30 105 below zero C.)

The usual arrangements of coolers as for example coils and heat exchangers are suitable for the cooling ofthe gases. It is particularly advantageous to add small amounts of solvent llo eiected Furthermore, it is preferable to cause the gas to flow upwards through the cool-- er, since in this manner the condensate ows in counter current to ,the gas current, namely downwards in the cooler into the warmer zone, whereby it" is prevented from becoming solid or pasty. The condensate is collectedin a separator outside the cooler but still within the insulation. Thus for examplethe condensate in the second stage of 'the cooling'assumes the temperature of the gas coming from the first stage, whereby it is warmed from to 30 below zero C. In this manner a new eiect is obtained, because the product liquefied in the colder zone contains acetylene dissolved therein and this is to a very great extent expelled at 30 below zero C. l

The gas obtained may be directly subjected to further chemical or physical treatment under pressure. Thus dilute acetylene purified according to the present invention may be enriched by washing with solvents under pressure and if desired at low temperatures.' The carrying out of this process of enriching the acetylene is con' siderably simplified by the gas puried at low temperatures; for` example the impurities in acetylene'from the electric arc lead to changes in the solvent which render a continuous operation impossible Without yintermediate complicated preparation of the solvent.

A greatv advantage of the process according to the present invention consists in the fact that the products separated are obtained in such a condition that they may be readily further worked up. On the contrary when activemasses alonev are employed for the purification, the products must be recovered again by a special process, whereby disadvantages by reason of vpolymerization and a consequent rapid impairing of the activity of .the active masses are not readilyavoided. Moreover, the waste of acetylene when working with active masses alone is con'- siderably greater than by the process according to the present invention.

A further ,advantage of the process according to the present invention resides in the fact that even with a varying content of impurities in the gas mixture, the gas obtained by the said treatment has a physically uniform degree of purity at the temperature employed, while the gas purifled for example by the employment of active masses, such Aas active carbon, may contain 'i different amounts of the said impurities dependingcn the degree of saturation of the active mass and the amount of impurities in the crude gas, whereby the Afurther working: up is injuriously affected.

Furthermore very as for example silica gel.

The linvention will be further explained with reference to the accompanying drawing showing a vertical section of a preferred arrangement little of the acetylene is lost by carrying out the purification in the` said suitable for carrying into effect the process accordingto the present invention. It is, however, to beunderstood that the invention is not restricted to the particular arrangement shown in the said drawing.

Referring to the drawing indetail numerals 1 and 2 denote two bundles of cooling tubes which are arranged in vessels 3 and4 respectively fllled with a cooling liquid. The said vessels are mounted in a heat-insulating box 5 which is lled with a suitable insulating materialf'such as'slag-wool or cork bricks. The initial acetylene gas to be purified is introduced, While at room temperature, at 6 into a vessel 7 filled with methanol and after being laden with vapours of methanol, passed to the collecting vessel 8 and from thence into the bundle of cooling tubes 1 communicating therewith in which it is cooled down in vessel 3 to about 30 below zero C. by means of crude methanol brought to "a temperature of about 35 below zero C. by expanding and vaporizing liquid ammonia in theA vaporizing coil 9. In-tubes 1 any moisture present in the acetylene gas is condensed together with the methanol vapours and, if any, with vapours of the solvent employed for concentrating the acetylene. The condensate collects in vessel 8 and may be withdrawn at 10. Also part of the unsaturated impurities is condensed in the upper part of the cooling tubes 1. These condensed impurities, however, are for the most part again vaporized when ilowing down into the less cold zones of the tubes. .The funcondensed gases having a temperature of about 30 .below zero C. are then led by way of pipe 11 into the collecting vessel 12 and from thence into the second bundle of cooling tubes 2 embedded in crude methanol which is cooled to about 75 below zero C. by expanding-and vaporizing liquid ethylene in the coil 13. The ethylene employed, before beingA expanded, is condensed'by passing it through a coil 14 advantageously arranged inI cooling vessel 3. In said tubes 2 the temperature of the acetylene gas is lowered from 30 below zero C. to about '70 below zero C. whereno by any unsaturated impurities are condensed together with traces of methanol vapours'still present in thel gas. The condensed constituents flow back into vessel 12 from which they may be withdrawn at 15. If any acetylene is con-.125 densed inthe upper parts o f the cooling tubes 2 it is vaporized again when flowing down into the lower less cold zones of these tubes, so that the liquid withdrawn at 15 is practically freefrom' acetylene whereas the acetylene gas leaving at -16 is, free from vany strongly unsaturatedV impurities... 'I'he methanol present in vessel 7 may bei replaced byy any other liquid readily giying `oif-`vapour`s and preventing from freezing ythe water condensed in` tubes 1 by dissolving it.

, The following examples will further illustrate the nature of this invention but the invention is riot restricted to these examples.

Eample 1 2.4 cubic metres per hour of a gas containing about 89 per cent of acetylene and ^4 per cent of diacetylene, allylene, allene and butadiene, the remainder being methaneand nitrogen, are passed at a speed of flow of about 25 centimetres 145 per second through an iron tube about 2 metres in length kept at about 30 below zero C. and then through a second similar tube maintained at a temperature ol' about 70 belowizero C. In this manner about 42 litres of gas per cubic metre 150 of the through-put are condensed in the second cooling stage (-115 cubic centimetres of condensate). Of this gas, 40 litres are the said impurities and 2fliimes are acetylene, i. e. about 0.1 per cent oi.' the purified acetylene.

The gas leaving the cooler is used directly for the preparation of acetaldehyde by the catalytic conversion of acetylene with steam. By working with the gas puried in the said mannerthe duration of the` activity of the catalyst is considerably lengthened and an excellent aldehyde is obtained. n

Example 2 2 cubic metres per hour of a gas consisting of about 9 per cent of acetylene, 0.4-per cent o! diacetylene, allylene, allene and` butadiene, 0.8 per cent of hydrogen cyanide, from 20 to 25 per cent of methane, from 2 to 9 per cent of nitrogen and the remainder oihydrogen are passed with a rate of ow o! about 10 centimetres per second u'ndei` a. pressure of about 25 atmospheres rthrough a cooler maintained at a temperature Vof 10 below zero C. and having a length'of about 180 centimetres. About 16.5 cubic centmetros of a liquid condensate, consisting of the impurities contained'in the gas and only traces of acetylene, are thereby condensed from each cubic metre of initial gas. The gas leaving the condenser is admirably suited for a further treatment as for example for -enrichmentin acetylene conversion into acetaldehyde.

/What we claim isz-- 1. Aprocess of increasing the concentration of acetylene in a gas mixture containing acetylene,

diacetylene,allene, allylene and butadiene, obtained by thermal treatment of a hydrocarbon above 1000 C. 'which comprises cooling the gas mixture to a temperature below 30 C. and continuing said cooling to a temperature approxi'- mately 70 C., such that the concentration of the acetylene in the gas is considerably increased,

but above the temperature at which acetylene is,

condensed. v f Y v 4 2. A process for yincreasing the concentration of acetylene in a gas mixture containing acetylene, diacetylene, aliene, allylene and butadiene, obtained -by thermal treatment of a hydrocarbon above 1000 C. which comprises cooling the gas mixture t a temperature of about -70 C.

3. A process for the purication of a gas comprising acetylene, diacetylene, aliene and butadiene, obtained by passing a vaporized hydrocarbon through an electric arc, from other strongly unsaturated compounds whichcomprises cooling the said gas tov a'temperature of about 30 below zero C. and then in a second stage to a tem perature of about 70 below zero C. HANNS BUECKERT. f

ROBERT STADLER. HELMUT IIJ'ANNEBEEtGfEl'x,.l

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